1. Field of the Invention
The present invention relates generally to ISDN telecommunications. In particular, the present invention relates to a method and apparatus for detecting a loopback condition on an ISDN PRI, and compensating for the loopback condition to prevent the failure of calls.
2. Background Art
Integrated Services Digital Network (xe2x80x9cISDNxe2x80x9d) has become increasingly popular in recent years, as use of the Internet and demand for digital communications among users has increased. ISDN offers users drastically increased data transmission rates compared to analog telephone lines. Additionally, ISDN offers capabilities that simply are not possible with conventional analog telephone service, such as fast call setup time, enhanced telephone functionality, and the simultaneous use of numerous types of digital services, such as telephone, fax, computer, or video conferencing, on a single ISDN connection.
While users are increasingly attracted to the capabilities of ISDN communications, it remains crucial for network service providers to uphold the expectation of reliability that users have developed with conventional analog telephone systems. Moreover, network downtime typically results directly in lost revenues for a service provider due to fewer billable connection completions. Accordingly, modern network service providers place great value on features that increase the reliability of a communications network, and reduce the number failed connection attempts.
Failed connections that many network service providers face is attributed to the necessary maintenance and testing of network transmission equipment. Network transmission equipment is commonly used for such purposes at the interconnection of multiple switching systems, or the multiplexing of numerous data lines onto a high-speed line for long-distance transmission. Typically, while transmission equipment undergoes maintenance or testing, ISDN Primary Rate Interface (xe2x80x9cPRIxe2x80x9d) connections are placed into a xe2x80x9cloopbackxe2x80x9d mode, in which data received by the transmission equipment on any PRI is immediately looped back out onto the same PRI, rather than being routed through to its intended destination. Because a PRI is a high-bandwidth connection, which typically contains communications from large numbers of users and services simultaneously, even a single looped-back PRI can result in service disruption to numerous users.
Traditionally, network service providers have attempted to reduce the number of aborted and/or incomplete calls due to maintenance and testing by reducing both the frequency with which maintenance and testing is necessary, and the time required to perform the necessary repair and maintenance activities. However, such efforts fail to prevent aborted calls and/or disrupted communications on those occasions during which hardware testing and maintenance is still required. Furthermore, in the event that maintenance personnel forget or otherwise fail to remove transmission equipment from maintenance mode upon completion of their activities, service may continue to be disrupted for a substantial time period.
Accordingly, it is an object of this invention to improve the reliability of ISDN communications by providing a method and apparatus whereby an ISDN communications system can detect when a PRI is in a loopback condition.
It is a further object of this invention to prevent the placement of outgoing calls onto a PRI that is in a loopback condition.
Yet another object of this invention is to allow the rerouting of calls from a looped-back PRI to a functional PRI.
It is also an object of this invention to implement the loopback detection and avoidance functionality in the switching system software to avoid the material expense of hardware upgrade and modification. Furthermore, it is intended that this invention will function properly with pre-existing network transmission systems without requiring upgrade or modification thereto.
These and other objects of the present invention will become apparent to those of ordinary skill in the art in light of the present specifications, drawings and claims.
The present invention includes a telecommunications switching system with one or more ISDN PRIs. Each PRI consists of a plurality of channels, according to the ISDN protocol. For each call initiated by the switching system, a call SETUP command is transmitted. Each call SETUP command is assigned a Call Reference Value (xe2x80x9cCRVxe2x80x9d) and requests a particular channel on the PRI.
Each time the switching system initiates a new call, the CRV assigned to the call SETUP command is stored as the Last Sent CRV. Upon receipt of an incoming call SETUP command, the switching system determines whether its CRV is the same as that stored as the Last Sent CRV. If an incoming SETUP is assigned the same CRV as the Last Sent CRV, and requests a channel on the PRI that is currently occupied, the incoming SETUP is considered likely to have looped back on the PRI.
Each time an incoming SETUP command is considered likely to have looped back on the PRI, a Loop Counter is incremented. When the Loop Counter exceeds a predetermined threshold value, the switching system determines that a loopback condition exists on the PRI.
The loop counter can be reset to zero when the switch receives positive indication that the PRI is not in a loopback condition. Such positive indications include the receipt of a valid response to an outgoing call SETUP command, the receipt on an incoming call SETUP command with a CRV differing from the Last Sent CRV, or the receipt of an incoming call SETUP command requesting a PRI channel that is not occupied.
When the switching system determines that the PRI is in a loopback condition, the PRI may be removed from service. The switching system does not attempt to initiate new calls on the PRI, and calls can be redirected onto alternative PRIs, if available. The switching system may thereafter attempt periodically to bring the PRI back into service, such that call traffic can resume upon correction of the loopback condition.